Production of heteropolysaccharide by fermentation of methanol

ABSTRACT

Disclosed is a new heteropolysaccharide polymer and a method for producing this polymer by a fermentation process comprising culturing a heteropolysaccharide-producing strain of a micro-organism of the genus Methylomonas on an aqueous culture medium containing methanol as the sole source of assimilable carbon. Several uses for the heteropolysaccharide are also disclosed such as its use as a drag reducing agent, a thickening agent, an emulsifier, a soil suspending agent and a flocculant or deflocculant.

BACKGROUND OF THE INVENTION

The present invention relates to the production of biopolymers and moreespecially to the preparation of polysaccharides by fermentation usingmethanol as the sole source of assimilable carbon. The invention alsorelates to the use of these biopolymers as drag reducing agents, asthickening agents, emulsifiers, soil suspending agents, flocculants ordeflocculants, etc.

Biopolymers have recently been the subject of increased research studiesbecause of the interesting properties exhibited by such polymers and thevarious applications suggested by these properties. The polysaccharideswhich have been studied most are those produced by fermentationutilizing bacteria of the genus Xanthomonas which generally utilizecarbohydrates as the source of assimilable carbon in a culture medium.These biopolymers act as versatile thickening agents for aqueous acids,alkalis and brines, and are good suspending agents for solids-in-waterand oil-in-water dispersions, and act also as excellent rheology controlagents. Thus, the xantham gums find application in oil well drilling mudsystems, as additives for secondary recovery of petroleum by waterflooding, and as stabilizers, emulsifiers and thickeners in foodproducts.

In view of economic considerations, however, it would be more desirableto employ petrochemicals as the source of assimilable carbonfermentation systems rather than carbohydrates. Of petrochemicals,methane or methanol would be the most economical. Some studies have beenmade on bacteria utilizing these compounds as a carbon source. Forexample, Leadbetter and Foster (Archiv fur Mikrobiologie, 30, 91-118,1958) isolated and grew several cultures of pseudomonads in a mineralsalts medium with methane as the sole source of carbon and energy.Harrington and Kallio (Can. J. Microbiol., 6, 1-7, 1960) have publishedwork on the oxidation of methanol by Pseudomonas methanica. But despitethe numerous studies on the specific activities of methane- andmethanol-utilizing bacteria and theorization as to the metabolicpathways, very little work has been conducted regarding characterizationof the biopolymers formed or in investigating the properties andutilities of these products resulting from fermentation in culture mediacontaining methane or methanol.

One factor prompting investigation of the properties of the biopolymersaccording to the present invention is that inexpensive conventionalpolymeric materials utilized in dilute aqueous solutions to produce adrag-reducing effect, such as polyethylene oxides and polyacrylamides,suffer from certain drawbacks. For example, these polymers arerelatively unstable to salt and acid or alkaline conditions, and theytend to breakdown in molecular weight during flow as a result ofturbulent conditions and moderate shearing forces. These disadvantageousfactors are also present in many of the polymeric thickening agentspresently being employed in drilling muds and flooding agents forsecondary recovery of oil in the petroleum industry.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process for theproduction of heteropolysaccharides through the fermentation of bacteriain a culture medium utilizing methanol as the sole source of carbon.

It is another object of this invention to provide a new polysaccharidehaving desirable properties.

Still another object of the invention resides in the production of animproved drag-reducing agent for use in dilute aqueous systems.

It is also an object of the present invention to provide an improvedthickening agent suitable for use in foods, cosmetics, paints, drillingmuds, and especially in flooding composition utilized in the secondaryrecovery of underground petroleum deposits.

A further object of the present invention is to provide a polysaccharidedisplaying improved properties for use as an emulsifier, a flocculent ordeflocculent and a soil suspending agent.

In accomplishing the foregoing objects, there has been providedaccording to the present invention a method for producing aheteropolysaccharide by fermentation which comprises culturing aheteropolysaccharide-producing strain of a microorganism organism of thegenus Methylomonas on a culture medium containing methanol as the solesource of assimilable carbon. The crude, cell-free polysaccharide, asprecipitated by acetone from the fermentation broth, contains from about60 to 90% by weight organic matter and from about 10 to 40% ash. Most ofthe latter consists of phosphates (15 to 25%) and cations (5 to 25%).The constituent sugars of the polymer are glucose (10 to 30%), galactose(3 to 15%) and mannose (3 to 15%) and the polymer contains a significantamount of pyruvic acid (5 to 35%). The crude polymer is negativelycharged and a 1% solution has a viscosity of 300-400 centipoise(Brookfield viscometer at 30 rpm). Fermentation is carried out at a pHbetween about 6.0 and 7.8 and preferably within the range of 6.2 to 7.5,and at a temperature between 25° C. and 33° C. The heteropolysaccharideproduced by this process exhibits excellent thickening and drag-reducingproperties when employed in dilute aqueous solution and is particularlystable to salts, acids, bases and to mechanical shear forces. Thepolymer finds many uses not only as a drag-reducing agent, but also as athickening agent in foods, cosmetics, paints, drilling muds, andespecially in water flooding compositions utilized for the secondaryrecovery of underground petroleum deposits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical plot of viscosity correlated with the weightpercent of biopolymer in aqueous solution;

FIG. 2 illustrates graphically the relationship between the viscosity ofan aqueous solution of polymer and both salt concentration and pH;

FIG. 3 is a graph showing the drag-reducing properties of thebiopolymers of the invention in relation to their concentration inaqueous solution; triangles represent a crude polymer containing cells,circles represent a membrane-filtered, cell-free solution.

FIG. 4 is a graphical plot of viscosity in relation to shear rate.

DETAILED DESCRIPTION OF THE INVENTION

The microorganisms employed in accordance with the present invention areof the type isolated by Tannahill and Finn from soil samples("Fermentation Process Based on Methanol", Paper presented to the 160thNational ACS Meeting, Chicago, Sept. 7, 1970). A specimen of thisparticular isolate has been deposited with the Northern RegionalResearch Laboratory of the U.S. Department of Agriculture in Peoria,Ilinois, and is identified by the number NRRL B-5696. A sample of thismicroorganism can be obtained from the aforementioned ResearchLaboratory. (The deposit was made with the understanding that allrestrictions on the availability to the public being irrevocably removedupon the granting of a patent.) Its mycological characteristics arepresented in detail below:

A. morphological observations

1. Salts-methanol (3% methanol) agar slant, 24 hours, vegitative cells,straight rods, 0.2- 0.4 × 1.0-2.0 microns, singly or in pairs, motile bysingle polar flagellum, no spore formation, gram negative.

B. cultural characteristics

1. Salts-methanol (3% methanol) agar colonies - 2 days, moderate toabundant growth, circular, pulvinate, smooth, glistening, entire,mucoid, yellow, medium unchanged.

2. Salts-methanol (3% methanol) agar streak - 2 days, moderate toabundant growth, filiform, smooth, glistening, bright yellow, butyrousto mucoid, medium unchanged.

3. Pigment does not diffuse into the medium.

C. physiological characteristics

1. Relation to free oxygen: strictly aerobic, pellicle formed in brothtubes, surface growth in agar stabs.

2. Temperature: optimum growth temperature, 28-30° C.; growth at 10° C.;no growth at 35° C.

3. pH for growth: optimum pH, 6.7 to 7.2; pH limits for growth 6.0 to7.8.

4. Catalase: positive (method of Skerman).

5. Gelatine hydrolysis: weakly positive after 24 hours (Key gelatinstrips).

6. Oxidase: positive (Key oxidase test tablets).

7. Pectinesterase: positive (method of McComb).

8. Nitrate reductase: positive (method of Skerman).

9. Growth in presence of 1% sodium chloride, but no growth with 2%sodium chloride.

10. Utilization of other carbon sources: no growth was detectedutilizing methane, formaldehyde, formamide, formate, ethanol,methylamine, glycine, DL-serine, succinate, D-glucose, fructose,glycerin or oxalate after a period of 48 hours had elapsed.

11. Litmus milk: no reaction.

12. No growth on nutrient agar, but no inhibition of growth if methanoladded to the nutrient agar.

13. Absorption spectrum of the carotinoid pigment is similar to that ofPsuedomonas methanica.

14. Yeast extracts and other vitamin mixtures do not stimulate growth.

15. Ammonium salts, nitrates, or urea serve as nitrogen sources. Otherorganic nitrogen sources can probably be used also.

D. source: soil

E. cell free extracts contained little HDP activity, but containedappreciable HPS activity according to the method of Kemp and Quayle.This suggests metabolism of methanol by the allulose pathway rather thanthe serine pathway.

The isolate of Tannahill and Finn exhibits certain similarities to thestrain identified as Pseudomonas methanica by Dworkin and Foster (J.Bact., 72, 646, 1956) but it is noted that differences exist: theisolate is not as phosphate sensitive, grows within a much narrower pHrange, does not grow on methane, and is more stable, i.e., does notexhibit the color variability reported for the known organism. No pinkor colorless variants of the isolate have been noted.

On the basis of the foregoing, it is concluded that the microorganism ofTannahill and Finn belongs to the genus Methylomonas, which has beendefined by Ribbons et al (Annual Review of Microbiology, vol. 24, pp.135-158, 1970) as follows:

1. Obligate methylotroph;

2. motile with polar flagellation;

3. rod shaped; and

4. forming only immature cyst.

The present organism, since it does not fall within any previouslydescribed species, has been designated as Methylomonas mucosa.

The broth medium utilized for growth of the microorganism consists ofthe following:

    ______________________________________                                        Material           Grams per Liter                                            ______________________________________                                        KH.sub.2 PO.sub.4  3.75                                                       Na.sub.2 HPO.sub.4 2.50                                                       (NH.sub.4).sub.2 SO.sub.4                                                                        2.00                                                       MgSO.sub.4.7H.sub.2 O                                                                            0.40                                                       Ca(NO.sub.3).sub.2.4H.sub.2 O                                                                     0.005                                                     FeSO.sub.4.7H.sub.2 O                                                                             0.005                                                     ZnSO.sub.4.H.sub.2 O                                                                              0.005                                                     ______________________________________                                    

This corresponds to the "minimal salts" formulations, except that in thepreferred embodiment a slightly higher concentration of calcium ions isemployed because it has been found that an increase in calcium ionsstimulates growth. Ammonium sulfate was the nitrogen source used formost of the work with this organism; however, it is also possible toutilize sodium nitrate and likewise obtain excellent growth. It wasfound that the organism can tolerate a methanol concentration of up toabout 7.0% by volume. The optimum growth occurred, however, withmethanol concentrations between about 0.5 and 5.0% by volume, whereasthe most preferred concentration is between about 2.0 and 3.0%.Similarly, it was determined that the pH value of the medium greatlyeffected growth, with no growth taking place below a pH of 5.7 to abovea pH of 8.0. Accordingly, a pH range of from about 6.0 to about 7.8 issuitable for growth of this microorganism, although a reasonable growthrate occurs only within the range of about 6.2 to about 7.5. Optimalgrowth takes place at a pH of approximately 7.0.

The cultivation procedure involves adding the salts to water in theabove listed order followed by pasteurization or autoclaving if desired.It is not absolutely essential that the culture medium be sterilizedprior to introduction of the microorganism since the organism is able togrow at such high methanol levels that there is not much competitionfrom other organisms. This is a distinct advantage as regards several ofthe particular use applications for which these microorganisms areespecially suited. Moreover, the property makes it possible to operatethe fermentation process as a continuous process. Methanol is then addedto the salt solution at approximately room temperature. When solid mediais desired to carry the organism, 1.75% Bacto Agar may be added to thesalts before pasteurization or autoclaving. Growth is carried outpreferably at about 30° C. in a shaker-incubator (controlledenvironmental incubator shaker, New Brunswick Scientific Company,Incorporated) utilizing one liter shaker flasks filled with from about200 to 400 milliliters of broth. Growth times are normally from about 48to 96 hours. After this period a highly viscous slime has been producedin the culture broth.

Recovery of the fermentation produce may be accomplished in conventionalways utilizing acetone, methanol, propanol, quaternary ammonium saltsets. as precipitants. Use of acetone has proven to be most appropriateaccording to the present invention. Accordingly the broth culture can befirst centrifuged for a period of from 10 to 20 minutes to remove someof the bacterial cells, and the clarified slightly yellow supernatantdecanted from the centrifuge to leave a cell pellet behind. To thissupernatant is added from 1.2 to 2.0 parts by volume of acetone,preferably 1.5 parts, per part of supernatant, and the mixture is wellmixed. The biopolymer is obtained as a light-colored cottonyprecipitate. It is then drained, placed into from 2 to 3 parts of freshacetone to remove as much water as possible, and finally dried at roomor elevated temperature to give a dry, powdery product. The averageyield of crude polymer after 48 hours, based on methanol used is about30 to 40 percent. About 10 to 15% of the methanol is converted to cellmass.

To determine the chemical identity of the biopolymer, a variety of testswere performed. By running a UV spectrum (Perkin Elmer No. 202Spectrophotometer) on the cell-free sample it is determined that thebiopolymer contains no protein or nucleic acids since there are no peaksat 280nm or 260nm. The tests for polybeta-hydroxybutyric acid isnegative (method of Law and Slepecky). The iodine test (method of Danieland Neal) indicates that the polymer is not starch or glycogen, whereasan ash test discloses that 37.4% of the crude polymer is inorganic. Aninfra-red spectrum suggests the presence of phosphate groups, carboxylgroups and possibly amine groups among the sugar molecules. The anthronemethod for total carboxydrate shows the crude polymer to contain from 20to 40 carbohydrate, and the Nelson method indicates a content ofreducing substances of 20 to 40%. Finally, all of the polymer isprecipitated from solution by the addition of a cationic detergent,cetyl trimethylammonium bromide. A table summarizing these results ispresented below.

                  TABLE 1                                                         ______________________________________                                        Assay          Result                                                         ______________________________________                                        (1) UV Spectrum                                                                              No protein or nucleic acids                                    (2) Polybeta-hydroxy-                                                                        Negative test                                                  buteric acid                                                                  (3) Iodine test                                                                              Not starch or glycogen                                         (4) Ash test   37.4% inorganic content                                        (5) IR spectrum                                                                              Presence of phosphate, carboxyl                                               and amine groups suggested                                     (6) Anthrone test                                                                            20 to 40% carbohydrate (based on                                              glucose); cationic detergent poly-                                            mer is negatively charged and                                                 precipitates completely                                        ______________________________________                                    

An elemental analysis performed on the biopolymer, twice reprecipitated,gives the following results:

    ______________________________________                                        Element      Per Cent By Weight                                               ______________________________________                                        P            6.24                                                             Ca           0.144                                                            K            12.00                                                            Mg           0.600                                                            Na           3.500                                                            N            2.00                                                                          Concentration ppm                                                Zn           356.0                                                            Mn           9.6                                                              Fe           77.6                                                             Cu           15.2                                                             B            5.6                                                              Al           135.2                                                            ______________________________________                                    

After acid hydrolysis, gas chromatographic analysis of the constituentsugars showed the following approximate molar ratios: glucose 1.5 - 2.0;pyruvic acid 1.5 - 2.0; galactose 1; mannose 1.

Some of the physical properties of the biopolymer were studied, forexample, solutions of the polymer were measured for viscosity at 25° C.under a variety of conditions. The measurements of viscosity were madewith a Brookfield viscometer at 30 r.p.m. in all cases. A curve showingviscosity (in centipoise) as a function of weight percent polymer ispresented in FIG. 1.

The intrinsic viscosity of the polymer in five percent sodium chloridewas 14.8 deciliters per gram, which indicates a fibrous rather thanglobular macromolecule of molecular weight in the range one to fivemillion. The effect of sodium chloride concentration on the viscosity ofa solution of polymer was tested by adding dry sodium chloride to a 1%solution of redissolved acetone-precipitated polymer. The curve in FIG.2 illustrates that the viscosity was stable over a wide range of saltconcentrations, a factor of significant importance in certain of theutility applications contemplated for the present biopolymer. Also, inFIG. 2 is shown the effect of pH on solution viscosity. These data wereobtained by the addition of potassium hydroxide or sulfuric acid toadjust the pH of 1.0% solutions of polymer in water. It can be seen thatthe viscosity rose from pH 7.0 to a maximum at pH 4.0, then declined asthe pH was lowered further. The viscosity gradually declined as the pHwas raised above 7.0. The addition of 10% sulfuric acid did nothydrolyze the polymer in solution whereas the addition of 10% potassiumhydroxide did.

The biopolymer according to the present invention were found to producea very interesting drag reduction phenomenon. Drag reduction experimentswere conducted on solutions of the biopolymer utilizing the techniquedescribed by Rodriguez in Engineering Education (to be published, 1973).The parameters adopted for the apparatus were as follows: reservoirheight = 4 feet, horizontal tube diameter = 0.29 cm., length ofhorizontal tube = 59 cm., vertical distance of effluent point tomeasuring point = 6 inches. In FIG. 3 is illustrated the reduction inthe friction factor of the polymeric solution as a function of weightpercent cell-free polymer at 30° C. Experiments were also conducted toverify the fact that the drag reduction occurred due to a true solutionof polymer and not due to particulates.

The biopolymer according to the present invention was found to becomparable in its drag reducing capability to the more conventionallyemployed polyethylene oxide and polyacrylamide polymers and also toother organic materials displaying drag-reducing properties, such ascarrageenan. Because of the cheapness and ready availability ofmethanol, which constitutes the sole source of carbon for the presentbiopolymers, there results a significant economic advantage to utilizingthe polymers of the present invention as drag-reducing agents as well asin other utilities. Moreover, whereas polyethylene oxide is subject tobreakdown in molecular weight during flow due to turbulent conditionsand therefore tends to degrade after one or two passes through a pipeflow system, the biopolymers of the present invention have been found tobe highly resistant to such shear degradation. Thus, a solution of thepresent polymer was passed through the test apparatus 15 times and nodegradation was observed. Exposure of a drag-reducing solution of theinstant polymer in a Waring blender for a period of 2 minutes degradedthe biopolymer, as would be expected, and the reduction in thesolution's friction factor was decreased significantly. FIG. 4illustrates the non-Newtonian property illustrated by a solution (10gm/l.) of the crude polymer.

The biopolymers of the invention have been found to be particularlyuseful in several types of applications. For example, as a result oftheir exhibition of drag-reducing properties in dilute aqueoussolutions, they are particularly suited for use in fire fightingequipment to enable propulsion of a stream of water over longerdistances, for addition to storm sewer systems in periods of heavy waterloads, for application to nautical vessels to assist in increasing speedthrough the water, for improvement of the operation of papermakingprocesses and for use in general in recirculating aqueous systems.Typically, the polymers are employed in an aqueous solution in aconcentration of from about 0.02 to about 0.20 grams per liter.

The biopolymers of the present invention are also useful as thickeningagents. In addition to finding utility as thickeners in conventionalapplications such as in foods, cosmetics, paints and the like, thepresent biopolymers have proved to be particularly well suited forvarious drilling field applications in the petroleum industry. Forexample, an excellent drilling mud is obtained when themucopolysaccharide is employed as a thickener in an amount of from about0.05 to about 3.0 percent by weight of the composition. Moreover,because the biopolymers of the present invention are anionic polymersand because they maintain their viscosity in the presence of sodiumchloride, they are particularly well suited for use in floodingcompositions employed in the secondary recovery of petroleum products insubterranean cavities. Also, because the fermentation process utilizedin the preparation of these biopolymers employs only an aqueous solutionof inorganic salts plus methanol, it is relatively insensitive to thecompetition of other microorganisms, and further, because methanolconcentrations can be made as high as 3-5% at which level most otherorganisms are inhibited, the present polymer lend themselves ideally topreparation directly in the drilling field, a location which is alsotypically close to an inexpensive supply of methanol. A typical floodingcomposition may contain between about 0.01 percent and about 1.0 percentby weight of the heteropolysaccharide of the invention. Thepolysaccharides of the present invention are employed in accordance withconventional principles, and for further information regarding the useof biopolymers in the aforementioned utilities, reference may be had toU.S. Pat. Nos. 3,020,207, 3,243,000 and 3,406,114. The presentbiopolymer is also useful as an emulsifier, flocculent or deflocculent,and as a soil suspending agent.

The following examples are included to more clearly illustrate theinvention, it being understood that the same are merely intended to beillustrative and not in any sense limitative.

EXAMPLE 1

350 milliliters of a culture broth having the following composition aresterilized for 20 minutes at 120° C.:

    ______________________________________                                        Material           Grams Per Liter                                            ______________________________________                                        KH.sub.2 PO.sub.4  3.75                                                       Na.sub.2 HPO.sub.4 2.50                                                       (NH.sub.4).sub.2 SO.sub.4                                                                        2.00                                                       MgSO.sub.4.7H.sub.2 O                                                                            0.40                                                       Ca(NO.sub.3).sub.2.4H.sub.2 O                                                                    0.025                                                      FeSO.sub.4.7H.sub.2 O                                                                            0.005                                                      ZnSO.sub.4.H.sub.2 O                                                                             0.005                                                      ______________________________________                                    

The above was mixed with 3% by volume of methanol, inoculated with thestrain Methylomonas mucosa and was cultivated with shaking at 30° C. for72 hours. The pH is metered constantly and appropriate amounts of KOH orH₂ SO₄ are added to maintain the pH at 7.0.

At the end of the fermentation time, the broth culture is centrifuged at20,000 g. for 15 minutes to remove some of the bacterial cells. Thenacetone is added in an amount of 1.5 volumes per volume of brothsupernatant obtained by decanting the clear, slightly yellow liquid fromthe centrifuge tube, leaving the cell pellet behind. The acetone-brothcombination is mixed well and cell-free polymer is recovered as alight-colored cottony precipitate. The polymer is drained, then placedinto 2 parts of fresh acetone to remove as much water as possible, andis finally dried at room temperature for 24 hours. 3.2 grams of thecrude solid polymer are obtained having an analysis as follows:

    ______________________________________                                        1. Organic matter 62.6%                                                       a. glucose 15.9%                                                              b. mannose 9.2%                                                               c. galactose 11.3%                                                            d. pyruvic acid 8.9%                                                          e. unidentifiables 17.3%                                                      2. Inorganic matter 37.4%                                                     a. phosphates 19.1%                                                           b. cations 18.3%                                                              ______________________________________                                    

EXAMPLE 2

The dispersant action of the biopolymer is demonstrated in a testwherein 0.2 gms ZnO powder suspended in 250 ml of distilled water wasallowed to settle in a graduated cylinder. After 30 minutes the upperlayer (5 ml sample) was tested for light transmission (Bausch and Lomb,Spectronic 20 meter).

    ______________________________________                                                           Optical Density                                                               Reading                                                    ______________________________________                                        No addition of biopolymer                                                                          0.24                                                     With 1 part biopolymer per 100                                                                     0.28                                                     parts ZnO                                                                     With 2 parts biopolymer per 100                                                                    0.40                                                     parts ZnO                                                                     ______________________________________                                    

While the present invention has been described hereinabove withreference to several specific embodiments thereof, it is readilyapparent that minor modifications, alterations and substitutions may bemade in the processes of preparing and using the subjectheteropolysaccharide polymer without departing from the spirit of thepresent invention. Therefore, it is intended that the invention belimited only by the scope of the claims appended hereto.

What is claimed is:
 1. A method of thickening an aqueous compositionwhich comprises adding to said composition from 0.1 to 3.0% by weight ofan heteropolysaccharide of bacterial origin having an intrinsicviscosity in the range of about 10 to 20 deciliters per gram andcomprising the following constituents on a weight per cent basis:1.Organic matter of 60 to 90% comprisinga. 10 to 30% glucose; b. 3 to 15%mannose; c. 3 to 15% galactose; and d. 5 to 35% pyruvic acid;
 2. 2.Inorganic matter of 10 to 40% comprisinga. 5 to 25% phosphates; and b. 5to 25% cations.
 2. The method according to claim 1, wherein said aqueouscomposition comprises a water flooding composition for subterraneanpetroleum-yielding formations comprising said polysaccharide in anamount of from 0.01 to 1.0% by weight.
 3. The method according to claim1, wherein said aqueous composition comprises an oil well drilling mudcomprising said polysaccharide in an amount of from 0.05 to 3.0% byweight.
 4. A water flooding composition for subterraneanpetroleum-yielding formations comprising an aqueous medium and fromabout 0.01 to 1.0% by weight of an heteropolysaccharide of bacterialorigin having an intrinsic viscosity in the range of about 10 to 20deciliters per gram and comprising the following constituents on aweight per cent basis:1. Organic matter of 60 to 90% comprisinga. 10 to30% glucose; b. 3 to 15% mannose; c. 3 to 15% galactose; and d. 5 to 35%pyruvic acid;
 2. Inorganic matter of 10 to 40 % comprisinga. 5 to 25%phosphates; and b. 5 to 25% cations.
 5. An aqueous oil well drilling mudcomprising an aqueous medium and from about 0.05 to 3.0% of anheteropolysaccharide of bacterial origin having an intrinsic viscosityin the range of about 10 to 20 deciliters per gram and comprising thefollowing constituents on a weight percent basis:1. Organic matter of 60to 90% comprisinga. 10 to 30% glucose; b. 3 to 15% mannose; c. 3 to 15%galactose; and d. 5 to 35% pyruvic acid.
 2. Inorganic matter of 10 to40% comprisinga. 5 to 25% phosphates; and b. 5 to 25% cations.